On Food and Cooking

Sour Cream Sour cream is essentially a
leaner, firmer, less versatile version of crème
fraîche. At around 20% milk fat, it contains
enough protein that cooking temperatures will
curdle it. Unless it is used to enrich a dish just
before serving, then, it will give a slightly
grainy appearance and texture. Sour cream is
especially prominent in central and eastern
Europe, where it has traditionally been added
to soups and stews (goulash, borscht).
Immigrants brought a taste for it to American
cities in the 19th century, and by the middle
of the 20th it had become fully naturalized as
a base for dips and salad dressings, a topping
for baked potatoes, and an ingredient in cakes.
American sour cream is heavier-bodied than
the European original thanks to the practice of
passing the cream through a homogenizer
twice before culturing it. A small dose of
rennet is sometimes added with the bacteria;
this enzyme causes the casein proteins to
coagulate into a firmer gel.